San Onofre: 100s of troubled tubes, gas leak

An assessment of a leaky steam-generator tube in one of the San Onofre nuclear plant's reactors won't be complete until next week, a spokeswoman for plant operator Southern California Edison said Friday.

And the company continues to examine similar tubes in a second reactor that was offline for maintenance.

The second reactor, known as Unit 2, has more than 800 tubes that showed wear and thinning, although they are only two years old, according to the Nuclear Regulatory Commission.

And plant officials confirmed earlier this week that sensors showed a tiny amount of radioactive gas may have leaked out of a building next to the Unit 3 reactor before it was shut down late Tuesday.

Edison workers are now trying to assess the extent and nature of the leak in one of Unit 3's steam-generator tubes.

All four of the plant's steam generators and their tubes are about two years old, installed after being delivered to the West Coast by the Japanese manufacturer of the generators, Mitsubishi Heavy Industries.

Some 9,700 tubes carry water from the reactor and through each generator.

"They have inspected 80 percent of the tubes in one of the steam generators at unit 2," said Victor Dricks, spokesman for the Nuclear Regulatory Commission. "Two of the tubes have thinning so extensive that they need to be plugged and taken out of service. Sixty nine other tubes have thinning greater than 20 percent of the wall thickness, and a larger number have thinning greater than 10 percent of wall thickness."

The tubes with 10 percent thinning number more than 800, he said.

Dricks and Edison spokesman Gil Alexander, however, said that highly sensitive alarms were tripped in an building next to San Onofre's unit 3 reactor after the leak was detected about 5:30 p.m. Tuesday, indicating that at least some radioactive gas was present.

The building houses the turbine that generates electricity.

Both Dricks and San Onofre officials said any release would have been extremely small, posing no hazard to workers or the public. Detectors elsehwere on the property picked up no signs of radiation above background levels.

"Had there been any change in radiation levels elsewhere in the plant, Edison would have immediately taken the appropriate steps, such as declaring the first of the four levels of emergency used by the industry," said Edison spokesman Gil Alexander.

Mitsubishi officials were on scene, he said, and there was no estimate of when the reactor might be started up again, though it will likely be several days.

“Mitsubishi is aware of the issue reported at the San Onofre Nuclear Generating Station and has been in contact with the customer, Southern California Edison," the company said in a statement released to the press. "The investigation of the incident is being conducted by our customer. However, as the manufacturer of the steam generators, we will do whatever we can to support our customer in resolving the issue.”

New details also emerged about an unrelated accident on Friday, when a contract worker slipped into a pool above the unit 2 reactor, now offline for maintenance, while trying to retrieve a flashlight.

The man, whose name Edison declined to release, was not injured, and did not suffer harmful radiation exposure, but might have ingested the mildly radioactive water, Alexander said. No internal contamination was found.

Normally, water that is heated by the reactor and flows through the tubes is kept separate from another loop of water, from another source, inside the steam generators.

Instead, the tubes are immersed in the water inside the steam generators, heating the water, which turns to steam that powers the plant's turbines to produce electricity.

But a small leak in one of the tubes could have allowed radioactive water circulating from the reactor to mix with the water in the steam generator.

If so, it could have resulted in the escape of a small amount of radioactive gas.

Although both of San Onofre's reactor units are now offline, with no word on how soon unit 3 can be restarted, Alexander said Edison has "ample reserve power" to supply customers.

He said such outages are planned for by the company, so would be unlikely to affect utility rates, at least in the near term.

Wearing and leaks in the tubes of pressurized water reactors are not uncommon, though typically occur after many years. About two-thirds of the nation's 104 nuclear plants use such systems, Dricks said.

Environmental groups began raising questions after the leak was first reported.

"It is certainly unusual to have hundreds of tubes damaged in new steam generators," said Daniel Hirsch, president of the Committee to Bridge the Gap, which closely monitors the nuclear industry. "Old steam generators, around 20 or 30 years, have some thinning on the tubes. What's puzzling and troubling is that this is brand new. It makes it sound as though there were deficiencies in the first place, or they were badly installed or horrendously maintained."

But Alexander said such wear is "not unprecedented in the first couple of years" of life for steam generators in the past. He said the new generators were rigorously tested both by Mitsubishi and again by Edison once they arrived.

It is not yet known whether the same type of wear reported by NRC in the unit 2 tubes is what caused the leak in unit 3.

Environmental groups also criticized San Onofre officials in November for delaying by an hour notification of the public about a non-radioactive ammonia leak in a storage tank that prompted some worker evacuations.

That leak also was described as posing no danger to the public, though it did prompt an alert, the second lowest of four emergency classifications. Tuesday’s unrelated steam-generator tube leak was not classed as an emergency.

San Onofre completed its $674 million steam-generator upgrade in 2010, with two of the behemoths replaced in each reactor.

Dricks said the most recent troubles do not seem to be a symptom of the plant's problems with personnel in past years, including some employees contending that they feared retaliation from management for raising safety concerns.

The NRC has said that Edison changed the safety culture sufficiently following those complaints.

But Hirsch said he was not so sure.

"San Onofre has had such a troubled history in terms of the safety culture that each of these incidents shakes me further," he said.

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